1. Field of the Invention
The present invention relates generally to a control system for resistance welding, and more specifically to an automatic welding voltage control system such that the welding voltage between a pair of electrodes can be controlled by changing the welding pressure or current applied to the electrodes in accordance with a reference voltage curve or a reference voltage integration curve.
2. Description of the Prior Art
In resistance welding, the welding quality is susceptible to change according to various welding conditions such as welding current, voltage, resistance, and the pressure between electrodes. Conventionally, therefore, there have been various testing systems for monitoring welding current, voltage, resistance, pressure, and so on between the two electrodes, and other systems for monitoring welded portions by using ultrasonic waves, for example, in order to check the quality of spot-welding. However, these monitoring methods or apparatus can only judge whether the quality of the welded portions is satisfactory after the welding process, and therefore cannot insure the quality of welding during the welding process.
With conventional resistance welding systems as explained above, therefore, if the welding is poor in quality, it is necessary to correct or repair the welded portion, or to discard the parts or products in the worst case where the welding quality is beyond repair.